Dynamic random access memory (DRAM) is a staple aspect of the main memory of PC systems. DRAM may be used as an embedded portion of an integrated circuit or be formed as an array of memory cells. Fir example, in memory cell arrays an MOS transistor and a capacitor make up a memory unit (cell) whereby word-lines are used to switch a pass transistor between an on and of state to connect the bit line to the capacitor or to isolate the capacitor. The bit line is used for both the read and write operations to the storage node of the capacitor.
Generally, three types of DRAM memory cells are in use including planar capacitor DRAM cells, stack capacitor DRAM cells and trench capacitor DRAM cells. A key element of DRAM devices is the scaling down of feature sizes to produce a smaller memory cell and allow the formation of a higher density of memory cells.
One challenge for increasing DRAM density is maintain the same cell capacitance as memory cell sizes are scaled down. Generally three approaches are available for doing this including increasing the dielectric constant of the capacitor dielectric, reducing the thickness of the capacitor dielectric, and increasing the area of the capacitor dielectric.
Prior art processes general use silicon on insulator (SOI) technology requiring complex formation processes to form the capacitor architecture together with the MOS transistors and bit and word lines that make up an operating memory cell. As DRAM memory cell sizes decrease, the formation of trenches and electrode materials is increasingly difficult due to small etching process windows and the difficulty in handling advanced electrode and capacitor dielectric materials.
Another problem with prior art approaches to producing DRAM devices is the inefficient use of active device area space, for example, in the substrate underlying the MOS transistor source and channel regions, frequently increasing the DRAM cell area by forming capacitors adjacent the bit and word lines and/or taking part of the drain area.
There is therefore a continuing need in the semiconductor manufacturing art including the IC memory manufacturing art for improved DRAM cell architectures including capacitor architectures and method for forming the same to reliably increase a capacitor area while efficiently utilizing active area space.
It is therefore an object of the invention to provide improved DRAM cell architectures including capacitor architectures and method for forming the same to reliably increase a capacitor area while efficiently utilizing active area space, while overcoming other shortcomings and deficiencies of the prior art.